Project Summary/Abstract High-density lipoprotein cholesterol (HDL-C) concentration is inversely associated with atherosclerotic cardiovascular disease (ASCVD) risk. However, recent data suggest that a measure of HDL particle function, HDL efflux capacity, may be a stronger predictor of ASCVD risk than HDL cholesterol level. HDL particles are composed of apolipoprotein A1 (apoA1) and enzymes embedded in a spherical phospholipid layer that surrounds a lipid core. One of the hypothesized protective functions of HDL particles is reverse cholesterol transport (RCT), which is the flux of cholesterol from peripheral tissues to the liver, where it is metabolized or excreted. HDL efflux capacity is the rate-limiting step of RCT. We hypothesize that variation in HDL efflux capacity is due to variation in apoA1 structure, which is a key mediator of this complex biochemical process. Top Down Proteomics is a novel technology, which allows for highly detailed characterization of apoA1 structural variants (proteoforms). The scientific aims of this K23 proposal are to: 1) define the spectrum of apoA1 and apoC3 proteoforms that are present in a sample of cohort participants and Northwestern outpatients, 2) determine the biologic variability of apoA1 proteoform expression over time, and 3) quantify the associations among apoA1 proteoforms, traditional risk factors, high-density lipoprotein (HDL) efflux capacity, and subclinical atherosclerosis. I am a practicing cardiologist and epidemiologist with interest in life course patters in cardiovascular disease and lipid-associated atherosclerotic cardiovascular risk. I currently hold a dual appointment in the Division of Cardiology and the Department of Preventive Medicine at Northwestern University Feinberg School of Medicine. Although I have training and expertise in long-term risk estimation and methods to describe patterns in cardiovascular risk across the life course, I aim to develop expertise in a molecular epidemiologic approach to quantifying lipid-associated atherosclerotic risk. To achieve the translational aims of this proposal I have assembled a mentorship and advisory committee of world leaders in in clinical lipidology, cardiovascular risk estimation, HDL biology and function, Top Down Proteomics, and biometric analytic approaches to proteomic data. As I work to achieve the scientific aims of this proposal, I will spend a total of 6 months completing informal tutorials in proteomics and HDL laboratories, attend multiple lipid-focused conferences, and complete coursework in bioinformatics. I have a formal system of evaluation arranged with all of my advisors and clear expectations for productivity and personal development have been established. Upon completion of this career development award I will be able to transition to become an independent molecular epidemiologist with a focus on lipid-associated atherosclerotic risk. I am confident that I can achieve the scientific and career development aims of this proposal and become an independent researcher leading collaborative research efforts between top-down proteomics researchers, lipid-focused basic scientists, epidemiologists, and clinical researchers to ultimately reduce the incidence of ASCVD.